Project Summary: Glioblastomas (GBM) are the most common and lethal primary central nervous system tumors. With the most aggressive therapy, median survival is 14.6 months. To date, there has not been a systematic approach to validate the function of candidate genes that are somatically amplified, for their role in glioma pathogenesis. These genes might play direct roles driving tumorigenesis, or tumor cells might depend on them for their survival and proliferation, a process known as "oncogene addiction." Therefore, these pathways are attractive targets for therapy. I performed an RNA interference screen targeting genes on regions commonly amplified in GBM and identified GEFT, a guanine nucleotide exchange factor (GEF), as essential for GBM cell proliferation and/or viability. Using genetic and biochemical approaches, I propose to characterize GEFT and its protein- protein interactions. I will test how suppression of GEFT regulates cell growrth and/or survival, and test if over-expression is sufficient to transform genetically well defined, immortalized astrocytes into a malignant glioma state. Additionally, I will determine the effector(s) of GEFT for cell proliferation and/or survival. Public Health Relevance: Glioblastomas (GBM) are the most common and lethal primary brain tumors. With the most aggressive therapy, median survival is 14.6 months. I propose to characterize a gene, GEFT, which might play a role in formation and maintenance of these tumors.